1. Field of the Invention
This invention relates to a process for preparing a soft, tinted lens. The process has particular, but not exclusive, utility in the preparation of contact lenses.
2. Description of the Prior Art
Soft contact lenses, for example, are commonly tinted so that they can be seen more easily during handling or to change or enhance the natural colour of the wearer's iris. Up until now, the processes commonly used for tinting lenses have been typically highly labour intensive processes that significantly increase the cost of manufacturing. In brief, the known processes involved placing hydrated lenses into a tint solution, then transferring them to a fixer solution and from there via a rinse solution to the inspection container.
An example of just such a process may be found in U.S. Pat. No. 4,891,046. This document discloses a hydrophillic (ie. a soft) tinted contact lens and a process for the preparation thereof. The lens, which is a copolymer, is first softened in a hydrating solution and then tinted by immersion in an aqueous solution of a reactive dye. The tint is then fixed by immersing the tinted lens in a fixing solution. Finally, the tinted lens is then inspected in an inspection solution.
These known processes, whilst enabling the production of soft, tinted contact lenses, suffer from a number of serious disadvantages.
Firstly, the use of a variety of different solutions (eg. hydrating, tinting, fixing, rinsing and inspection solutions) greatly increases the quantity of labour required in the preparation of the lens, and hence also increases the cost of the lens.
Secondly, as the lens is moved a number of times and immersed in a number of different solutions and containers, the likelihood of handling damage being inflicted upon the lens is dramatically increased.
Finally, the step of tinting a hydrated lens in a separate tinting solution has been found to produce lenses that often have an inconsistent tint. In other words, it has been noted that the colour of a tinted lens is often not consistent across its entire surface. It has also been noted that successive lenses may have varying colour tints.
The present invention seeks to alleviate some or all of the problems associated with the known processes.